GitLab

The event source based on FD watcher had wrong priority, which resulted in that
GDK and GTK events stuck forever, and GTK dialogs won't show up.

This CL fixes the priority of the FD watcher source to be higher than the one
for the main work source, and also enables the GTK file selection dialog in
Ozone builds.

The implementation currently requires use_glib=true.  There are other things
(e.g., dialog modality) that will be fixed in subsequent CLs.

R=kylechar@chromium.org, thomasanderson@chromium.org

Bug: 1008755
Change-Id: I673cff846ea6d03db25190481fe391b4c6e76650
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1892954Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Alexander Dunaev <adunaev@igalia.com>
Cr-Commit-Position: refs/heads/master@{#713089}